1. Field of the Invention
The present invention relates to an adaptive echo canceller technique used in communications equipment. More particularly, the invention relates to a testing method and device which are preferable to make sure of a function of an echo canceller.
2. Description of the Related Art
FIG. 10 shows arrangement of a testing system used for making sure of a function of an echo canceller contained in the conventional communications equipment. As shown, 11 is an echo canceller, 101 is a white noise generator, 102 is a level detector, 103 is a delay circuit, and 104 is an attenuator. The arrangement is defined according to the echo canceller and its relevant testing method discussed in CCITT Recommendation G. 165, (red book) pp 258-279. FIG. 2 is a block diagram showing basic arrangement of the echo canceller shown in FIG. 10. As shown in FIG. 2, 21 is a tap coefficient updating unit, 22 is a tap coefficient memory, 23 is an echo estimator, 24 is a far-end talker signal memory, 25 is a double talk detector, 26 is a subtracter, and 27 is a center clipper.
In order to make sure of a function of the normal echo canceller 11 under the foregoing arrangement, as shown in FIG. 10, the echo canceller 11 is connected at a terminal 3a to the white noise generator 101 in a manner to receive an output signal r(n) from the generator 101 and connected between terminals 3b and 3c to the delay circuit 103 and the attenuator 104 for simulating an echo path in a manner to receive an output signal s(n) from the attenuator 104. Under the connecting arrangement, the echo canceller 11 serves to send an output signal e(n) to the level detector 102 for detecting a residual echo level of an output signal e(n) from the echo canceller 11. The prior art relevant to detection of an echo canceller is discussed in JP-A-63-42528 and Dutteiler et al. "A single-chip VLSI Echo Canceller", the Bell System Technical Journal, Feb, 1980, pp 149-160.
The aforementioned prior art does not offer a simple function-testing method the echo canceller itself can realize. That is, it is necessary to connect the white noise generator 101, the level detector 102, the delay circuit 103, and the attenuator 104 to the echo canceller 11. Besides, the testing method requires disabling a call/talk alive in the echo canceller 11 for doing the test. It results in being unable to do a function test while a talk is alive.